Gas turbine engine discharge nozzles may include variable area and/or variable direction flaps. Such flaps are substantially planular and rotate between opposed parallel side walls of the nozzle.
The flaps must tolerate high temperatures in the order of 1500 F. during high power operation, but experience only lower temperatures at other conditions. It is conventional to supply cooling air to the exposed surfaces of the flaps at locations within the nozzle. Cooling air quantities which are required at high power are wasteful and unnecessary at other conditions, since such cooling is not needed and the air bypasses the turbine thereby resulting in decreased power.
The trailing edge of each flap is not exposed to the mainstream gas flow as it passes through the nozzle. However, the hot mainstream gas will eddy as it leaves the nozzle and reattach to the downstream edge of the nozzle, resulting in overheating. Such overheating may not only lead to failure of the liner surface itself but radiation from the hot surface may damage internal structural members which are not tolerant of such high temperatures.